Contra-resonant anvil

ABSTRACT

Apparatus and method are disclosed for welding metal members by means of vibratory energy. Reliability of such welding apparatus is improved by provision of an anvil designed for regulated response to excitation by an ultrasonically-powered sonotrode. The anvil is mounted in an assembly which contributes appropriate support, restraint and isolation.

United States Patent 15 3,695,500 Walraven et a1. Oct. 3, 1972CONTRA-RESONANT ANVIL [56] References Cited [72] Inventors: Thomas A.Walraven; Nicholas Maropis; both of West Chester; UNITED STATES PATENTSWIlliam C. Elmore, Swanhm r 3,184,841 5/ 1965 Jones et a1 ..29/470 JanetDevine, West Chester, all of 3,257,721 6/1966 Jones ..29/470.l Pa.3,341,935 9/1967 Balamuth ..29/470 [73] Asslgnee: Aeropro ec'tsIncorporated, West Primary Examiner john R Campbell Chester, Pa.Assistant Examiner-R. J. Craig [22] Flled June 1, 19 0 Attorney-Seidel,Gonda & Goldhammer. [21] App1.No.: 42,518

[57] ABSTRACT 1 Related Apphcauon Data Apparatus and method aredisclosed for welding met-a1 Continuation-impart 0f members by means ofvibratory energy. Reliability of March 1968, abandonedsuch weldingapparatus is improved by provision of an anvil designed for regulatedresponse to excitation by U-S. Cl- 3 an ultrasonically powered sonotrodeThe any is s ..B23k m ted in an assembly contributes ap- [58] Field ofSearch ..74/l, l R, 1 SS; 228/1;

propriate support, restraint and isolation.

8 Claims, 3 Drawing Figures PATENIEmm I972 IIIIIIHII IlllllllCONTRA-RESONANT ANVIL This application is a continuation-in-part of ourcopending application Ser. No. 717,295 filed Mar. 29, 1968 nowabandoned.

Vibratory welding process and apparatus have been described in US. Pat.No. 2,946,l l9 entitled Method and Apparatus Employing Vibratory Energyfor Bonding Metals" issued July 26, 1960, in the names of James ByronJones William C. Elmore and Carmine F. DePrisco. The disclosures in saidpatent are incorporated into the subject patent application and made apart hereof.

Ultrasonic welding in accordance with the present invention may beeffected under the conditions generally developed and set forth in theaboveidentified patent. As described therein, the materials to be weldedare clamped in the welding machine between a transducer-driven sonotrodeand an opposing member, or anvil. The two workpiece surfaces to bejoined are clamped together at the intended weld zone with a staticforce sufficient to hold the pieces together and assure that vibrationdelivered by the transducerdriven sonotrode will produce welds resultingfrom the cyclic stresses in the weld zone.

It will be understood by those familiar with ultrasonic welding that ifthe microdisplacements and interfacial stresses associated with weldingare maximum, then energy delivery to the weld locale will be maximum.The sonotrode-opposing, work-supporting member, hereinafter referred toas the anvil, is significantly involved with the capability of thewelding apparatus to deliver power to the weldment locale and producesuperior welds with minimum power.

Reliability and reproducibility of performance of vibratory weldingequipment has occasionally been hampered by anvil difficulties. Varyingperformance has sometimes been attributed to the supporting structuresof anvils, to their attachments to the primary structures of the weldingmachine, and to varying elastic compliance of the anvils themselves.

The need for designable anvils with predictable characteristics has beenincreasingly evident as equipment of greater precision, higher power, orotherwise generally improved capability has been developed and utilizedin production. Anvil problems during pre-shipment performance checkoutof ultrasonic welding machines have sometimes consumed excessive timeand been reflected in increased equipment cost. Yet as far as is known,no completely practical, design-optimizable, non-powered anvil apparatusand/or method have heretofore been developed as a solution to theabove-described ultrasonic welding machine problems.

Consideration of ultrasonic welding has led to an accepted. view that,for best welding performance, the amplitude of the sonotrode tip shouldbe maximum under the power delivery conditions of welding. Regardingdesirable function of the anvil, two views have been prevalent one, thatthe anvil should preferably be subject to powered vibratory excursionswhich are out-of-phase with the vibratory excursions of the sonotrodetip, and the second, that when a powered anvil could not be provided,the anvil should be generally passive, i.e., non-compliant or dead-beat.

It has long been known that ultrasonic welding can be enhanced byout-of-phase excursioning in both the sonotrode tip and theanvil, acondition which can be accomplished by appropriately powering the anvilmember as well as the sonotrode. The power-driven anvil approach,however, requires an additional transducer-coupling device and istherefore complicated and more costly; practicality usually prescribesuse of systems wherein power delivery to the work is by one poweredsonotrode only.

As to the acoustic reaction of non-powered anvils, a generally-heldbelief has been that maximum welding effect was realizable when theanvil was, as stated above, virtually passive in response to vibratoryforces imposed by the sonotrode tip. Following this approach, effort hasfrom time to time been expended toward maximizing the passive, ordead-beat characteristics of ultrasonic welding anvils and theirsupports. Although it was recognized during these efforts that the anvilwould necessarily be elastic within the normal range of its materialproperties, the potential role of the natural elastic vibration of theanvil has heretofore not been adequately understood.

The present invention is based on the discovery that essentially passiveor dead-beat anvils do not produce optimized welding machineperformance, as evaluated by thicknesses of materials successfullywelded and the power-time relationship needed for welding same. It hasobserved, on the contrary, that substantially improved weldingperformance can be effected when the anvil vibrates, and withconsiderable intensity, during the accomplishment of an ultrasonic weld.It was since postulated that the enhanced welding effect is derived fromperiods of out-of-phase excursion of the anvil tip with reference to theexcursions of the sonotrode tip during the interval used to accomplish avibratory weld a circumstance intermittently resembling that whichoccurs continuously when both the anvil and sonotrode are powered, ashereinabove discussed. it was further postulated that the elasticcompliance of the anvil is related to a vibratory response of the anvilto the excitation by the sonotrode.

Frequency response in resonant anvils has been considered previously forinstance, it has been shown that when the anvil response to thesonotrodes vibration occurs at the same frequency as the operatingfrequency of the powered transducer-coupling system, or in overtonesthereof, welder performance is adversely affected. This effect has beenacknowledged previously, as in the hereinabove referenced US. Pat. No.2,946,l 19, but elimination of adverse anvil performance in a specificwelding machine has generally involved only experimental adjustments ofanvil dimensions.

Investigation and analysis associated with the present inventionrevealed that much improved reproducibility of welding performance aswell as actually stronger welds are accomplished when the anvil has aresonant frequency somewhat above, or somewhat below, the operatingfrequency of the powered transducercoupling-sonotrode system of thevibratory welding machine.

It was further observed that an anvil of desired contra-resonantcharacteristics presents a high driving impedance at the operatingfrequency of the transducercoupling system, and that impedance valuescould be employed in dimensioning the anvil for regulated responsewithin a range of acceptable frequencies.

Thus the object of the present invention is to provide novel anvilapparatus and method of using the same in ultrasonic welding.

It is another object to provide ultrasonic anvil apparatus and methodwherein a non-powered anvil reed is subject to excursions which areout-of-phase withexcursions of the welding sonotrode over a substantialportion of the weldinginterval. I

It is another object to provide a novel anvil which can be acousticallydesigned to overcome problems encountered heretofore in the performanceof an ultrasonicwelder.

It is another object to provide a novel reactive element for use in anultrasonic apparatus such that said element is induced to vibration byand out of phase with an exciting member or members of said apparatusduring a significant portion of the interval of applied vibration.

Other objects appear hereinafter.

There is shown in the drawings an embodiment of a vibratory anvilapparatus which exmplifies the present invention. It must be understoodthat the invention is not limited to the embodiment here presented or tothe precise arrangement and instrumentalities shown.

Having these qualifications in mind and referring to the schematicdrawings wherein like reference characters refer to like parts:

FIG. 1 is a perspective view of an exemplary anvil apparatus designedfor use with an ultrasonic welding machine in accordance with thepresent invention.

FIG. 2 is a sectional view of the apparatus taken across line 2-2 ofFIG. 1.

FIG. 3 is an exploded perspective view of the components of theapparatus depicted in FIGS. 1 and 2.

Referring conjointly to FIGS. 1, 2 and 3, all of which portrayan anvilapparatus designated as 50, it should be initially understood thatfixed-free reflective anvil 10 is the critical member of apparatus 50and that its design characteristics establish general requirements forother members of an effective assembly. Anvil reed l and base ring 12 towhich it is attached most fundamentally embody the novel reciprocalfunction of apparatus 50 with a cooperating ultrasonic welding machine.Otherwise apparatus 50 is comprised of various mechanical elements whichserve as practical hardware for the support, restraint, and isolationrequired to assure the functionof apparatus 50 in accordance with thepresent invention.

- Referring now to the drawings in detail, in FIG. 1 the anvil reed isshown assembled into a work support apparatus of a typecharacteristically employed with ultrasor'iic welding machines. Readilyidentifiable components in the FIG. 1 perspective view include anvil 10which is shown attached into base ring 12 which restrains anvil 10.Anvil l0 and ring l2-are preferably metallurgically attached asbybrazing. The assembly of anvilv 10 and ring 12. may be removablyattached to flange 18a of a support mass 18 by means of bolts such as80, 8b, 8c and 8d. An isolated support mass 18 may be housed within thebore of block support member 24 which is shown mechanically attached tothe frame 15 of the welding machine "by bolts 7a and 7b which penetratethe frame 15-.

Structural details may be morecompletely identified by consideringconjointly FIGS. 2 and '3. Anvil l0 preferably includes a hardened"work-"contacting face member 10a which may either be screw-attached orpreferably metallurgically a'ttachedas by brazing to anvil 10. Whenutilized as a detachable element, the hardened tip l0ais'included as anintegralpart of anvil 10 in calculations pertinent to o'verallanvildesign. The base' portion of anvil I0 is preferably metallurgicallybonded, as by brazing, at jointure interface 11, into base ring 12. Thefunction of ring 12 is to support and provide a degree of clampingaction on anvil 10 which will assure a desired vibratory condition ofanvil 10 as it vigorously contra-resonates in response to appliedforcesfrom the active sonotrode 23 of a welder.

A series of elastomeric gasket-like components having as their purposethe prevention of metallic contact between the support mass 18 and blocksupport 24 are .shown. Top isolator gasket 20 is interposed at theinterface between flange 18a and block support24. Anvil support 24 maybe grooved circumferentially at an upper and lower location of the bore25 for retention of upper and lower O-ring elastomeric isolators 22 and26 which serve to prevent metal contact between wall areas of mass 18and block support 24 and thereby acoustically isolate mass 18 fromsupport 24. Bottom elastomeric disk 28acoustically isolates the support24 from steel clamping plate 30. I

Mass 18 is retained in block support 24 by the bolt 34. Bolt 34 extendsthrough washer 32, clamping plate 30 and elastomeric disk 28 into atapped hole in mass 18. It will be seen that tightening of bolt 34 willhave the effect of drawing the flanged mass 18 down toward block support24. Elastomeric member 20 acoustically isolates flange 18a and support24.

It will be noted that sonotrode 23, anvil 10, ring 12 and mass 18 areshown to be coaxial, but such coaxial arrangement is not mandatory;moreover, it should be clearly understood that the anvil of the presentinvention is altogether useful and effective with the severalembodiments of ultrasonic welding apparatus depicted in FIGS. 1, 3, 6,and 8 of US. Pat. No. 2,946,119.

It has been stated hereinabove that anvil 10 is the critical member ofapparatus 50 and that its design characteristics establish designrequirements for other members of the assembly. The general method fordimensioning an anvil reedfor appropriate contraresonance includesthesteps of (1) calculating anvil impedance as related to elasticcompliance factors, viz., transverse stiffness andbase rigidity, 2)integrat ing the aforesaid calculations with additional impedancecalculations relating to anvil reflectivity of vibrations, and(3)translating the above impedance calculations into anvil dimensionsproductive of a frequency response in the anvil which will be out-of-vphase with that of the cooperating sonotrode during a substantialportion of the weld cycle. t

The design of the contra-resonant or high-impedance anvil reed 10 isbased upon the operating frequency and acoustic powerv capability of thewelder. If a flexural contra-resonantfrequency response is desired inanvil reed 10 (as, for'example', for -use-in an ultrasonic apparatuswhich delivers vibratory energy in the shear mode, the' length of theanvil feed is determined by the equation:

can be determined from the roots of the transcendental equation:

, tanhatana= (2) Solution of equation (2) and substitution in equation(l) defines the contra-resonant or highimpedance characteristics for theanvil reed 10. Suitable roots of this equation are a, 51r/4 a 97r/4 and(1;, 131/4 ;etc.

The anvil described above relates to an anvil which is designed torespond in flexure. The concepts of the present invention areequallyapplicable to anvils which respond either axially(longitudinally) or torionsally.

If an axial contra-resonant frequency response is desired in anvil reed10 (as, for example, for use in an ultrasonic apparatus which deliversvibratory energy in the axial, or longitudinal mode), the length of saidanvil reed is determined by the equation:

L a (C /w) wherein L is the length of the anvil 10 in inches, 0,, is thelongitudinal velocity of the sound in the anvil reed, w is the angularfrequency 21rf and f is the operating frequency of the welder, and a isa function of impedance and can be determined from the roots of thetranscendental equation:

c a 0 4 Suitable roots of the equation are a= IT/2, 31r/2, 51r/2, 711/2,etc.

If a torsional contra-resonant frequency response is desired in anvilreed 10 (as, for example, for use in an ultrasonic apparatus whichdelivers vibratory energy in the torsional mode), the length of saidanvil reed would be determined by the equation:

("sh0ur/ where L is the length of the anvil in inches, to is the angularfrequency 21rf and f is the operating frequency of the welder, shear isthe shear velocity of sound in the anvil, and a is a function ofimpedance and can be determined from the roots of the transcendentalequatron:

cota= 0 (6 Suitable roots of this equation are: a =1'r/2, 31r/2, 51r/2,71r/2,etc. Solution of equation (6) and substitution in equation (5)defines the contra-resonant or high impedance characteristics for theanvil reed 10 operating in the torsional mode.

It will be recognized by those skilled in the art that an anvil reeddesigned according to the foregoing equations will have an effectivelength somewhat greater than its physical length due to non-idealboundary conditions, particularly compliance at its fixed end. However,since the foregoing equations are well known, it is expedient to usethese equations for reproducibly designing anvil reeds, but in practiceit may be necessary to modify the length somewhat to achieve the desiredcharacteristics of moderately high impedance and amplitude which yieldoptimum performance.

The diameter for each anvil reed described above is based upon thereference diameter of 1.65 inches which has been found adequate forultrasonic systems of up to 1,000 acoustic watts power capability. Thediameter d for anvils for any power level P, can be determined from theequation:

d =0.294 P, (7) Thus, for a 15 kHz welder of 4,000 acoustic watt powercapability, the diameter d, is attained from equation (7) as follows:

d ,=0.29 4/ 4,000=0.29 X 7.98=2.3l inches Hence, from equation (1) for atool steel reed anvil, wherein m 9.42 X 10 sec c 2.04 X 10 in/sec; K=0.578 in; and 0: 91r/4, the length L is approximately 7.92 inches. Itshould be noted that any of the roots of equation (2) satisfies therequirements; however, more practical length values are achieved for thefirst four roots, i.e., a. .01

The following chart summarizes suitable dimensions for the relevantcomponents which have been acoustically determined in accordance withtwelve operative embodiments and are for illustrative purposes only. Insaid chart, L represents the length of anvil reed 10, H

represents the height of ringl2 and of mass 18, and d represents theirdiameters.

Welder Fre- Power Anvil Reed 10 Ring 12 Mas l8 quen- (watts) L, L,, d Hd H d d y ("l ("l (")("l ("l l") foregoing specifications as indicatingthe scope of the invention.

We claim:

1. Anvil apparatus comprising an anvil reed free on one end andconnected at its other end to a mass, a support for said mass and anvilreed, the length of the anvil reed being substantially defined by:

wherein K is the radius of gyration r/2 of the anvil reed section wherer is the radius of the reed, w is the angular frequency 21rf where f isthe operating frequency of the welder, 0,, is the longitudinal velocityof sound in the anvil reed, a is one of the roots of the transcendentalequation: tanha tana 0, and the diameter d, of the anvil reed is definedby:

wherein P, is the desired acoustic power level at which the anvil is tobe used.

2. Anvil apparatus in accordance with claim 1 including a base ringforming a portion of said mass, said anvil reed being connected at itslower end to said base ring. v

3. Anvil apparatus in accordance with claim 1 wherein said mass isacoustically isolated from said support by an elastomeric material.

4. Anvil apparatus comprising an anvil reed free at one end andconnected at its other end to a mass, a support for said mass and anvil,said mass being acoustically isolated from said support, the transversedimens'ion of the anvil being defined by:

d',=0.29 V R r wherein P, is the desired acoustic power level at whichthe anvil is to be used.

5. Anvil apparatus is accordance with claim 4 wherein said anvil isinduced to respond in the flexural mode so that the length of the anvilis defined by:

dental equation: tanha tana 0.

6. Anvil apparatus in accordance with claim 4 wherein said anvil isinduced to respond in the axial, or longitudinal, mode so that thelength of the anvil is defined by:

where L is the length of anvil in inches, c is the longitudinal velocityof sound in the anvil, w is the angular frequency 21rf and f is theoperating frequency of the welder, and a is one of the roots of thetranscendental equation: cota 0.

7. Anvil apparatus in accordance with claim 4 wherein said anvil isinduced to respond in a torsional mode so that the length of the anvilis defined by:

L shear/ where L is length of anvil in inches, to is angular velocity21rf and f is the operating frequency of the welder, c is the shearvelocity of sound in the anvil, and a is one of the roots of thetranscendental equation: cota 0.

8. Anvil apparatus in accordance with claim 4 wherein said anvil reed isconnected to the mass by means of an annular base, the.base being boltedto the mass, the anvil reed extending through a central bore in thebase, said anvil reed being metallurgically bonded to said base.

1. Anvil apparatus comprising an anvil reed free on one end andconnected at its other end to a mass, a support for said mass and anvilreed, the length of the anvil reed being substantially defined by: LAlpha square root K co/ omega wherein K is the radius of gyration r/2 ofthe anvil reed section where r is the radius of the reed, omega is theangular frequency 2 pi f where f is the operating frequency of thewelder, co is the longitudinal velocity of sound in the anvil reed,Alpha is one of the roots of the transcendental equation: tanh Alpha -tan Alpha 0, and the diameter dx of the anvil reed is defined by: dx0.29 cube root Px wherein Px is the desired acoustic power level atwhich the anvil is to be used.
 2. Anvil apparatus in accordance withclaim 1 including a base ring forming a portion of said mass, said anvilreed being connected at its lower end to said base ring.
 3. Anvilapparatus in accordance with claim 1 wherein said mass is acousticallyisolated from said support by an elastomeric material.
 4. Anvilapparatus comprising an anvil reed free at one end and connected at itsother end to a mass, a support for said mass and anvil, said mass beingacoustically isolated from said support, the transverse dimension dx ofthe anvil being defined by: dx 0.29 Cube Root Px wherein Px is thedesired acoustic power level at which the anvil is to be used.
 5. Anvilapparatus is accordance with claim 4 wherein said anvil is induced torespond in the flexural mode so that the length of the anvil is definedby: L Alpha Square Root K co/ omega where L is length of anvil ininches, K is the radius of gyration r/2 of the anvil reed section wherer is the radius, omega is the angular frequency 2 pi f and f is theoperating frequency of the welder, co is the velocity of sound in theanvil, Alpha is one of the roots of the transcendental equation: tanhAlpha - tan Alpha
 0. 6. Anvil apparatus in accordance with claim 4wherein said anvil is induced to respond in the axial, or longitudinal,mode so that the length of the anvil is defined by: L Alpha co/ omegawhere L is the length of anvil in inches, co is the longitudinalvelocity of sound in the anvil, omega is the angular frequency 2 pi fand f is the operating frequency of the welder, and Alpha is one of theroots of the transcendental equation: cot Alpha
 0. 7. Anvil apparatus inaccordance with claim 4 wherein said anvil is induced to respond in atorsional mode so that the length of the anvil is defined by: L Alpha(cshear/ omega ) where L is length of anvil in inches, omega is angularvelocity 2 pi f and f is the operating frequency of the welder, cshearis the shear velocitY of sound in the anvil, and Alpha is one of theroots of the transcendental equation: cot Alpha
 0. 8. Anvil apparatus inaccordance with claim 4 wherein said anvil reed is connected to the massby means of an annular base, the base being bolted to the mass, theanvil reed extending through a central bore in the base, said anvil reedbeing metallurgically bonded to said base.